Fluid end with removable dual-valve cartridge

ABSTRACT

A fluid end assembly is described herein with a flow box having an inlet manifold having an inlet opening, an outlet manifold having an outlet opening, and a housing between the inlet manifold and the outlet manifold; and a valve cartridge removably disposed in the housing. In one embodiment, the valve cartridge includes a sleeve with a first end and a second end; a valve seat at each of the first and second ends; a first valve disposed in the sleeve at the first end; and a second valve disposed in the sleeve at the second end.

FIELD

Embodiments described herein relate to fluid ends for high pressure pumps.

BACKGROUND

High pressure pumps used in industries such as oil and gas have a plurality of linear force members, such as pistons or plungers, coupled to a crankshaft that rotates to cause the linear force member to reciprocate. The linear force member heads extend and retract inside a fluid end that channels the fluid flow powered by the linear force members. The flow channel of the fluid end is typically perpendicular to the stroke axis of the linear force member. During the suction phase of the stroke, the linear force member retracts producing a vacuum inside the fluid end. A suction valve inside the fluid end on the inlet side has fluid pressure on one side of the valve and internal pressure of the fluid end on the other side. As the linear force member retracts, declining pressure on the internal side of the suction valve causes the suction valve to retract, allowing fluid into the fluid end. During the power phase of the stroke, the linear force member then advances raising the pressure on the fluid in the fluid end. The pressure reseats the suction valve, closing the inlet side of the fluid end. A discharge valve inside the fluid end on the discharge side has line pressure on the outside of the valve and internal pressure of the fluid end on the inside of the valve. As the linear force member increases pressure inside the fluid end, the discharge valve opens, allowing fluid from the fluid end to flow through the valve into the line, exiting the fluid end. The stroke then repeats, with the discharge valve closing and the suction valve opening again.

The valves must seat and seal during each stroke to avoid fluid flow in the wrong direction. Typically, the valves use springs to bias each valve closed. Spring constants are chosen such that pressures developed upstream, downstream, and within the fluid end cause the valves to open at appropriate times and the springs cause the valves to close when the pressure equalizes. The valves are typically held in place by a fluid end cap that fastens to the fluid end and seals fluid into the assembly.

In conventional fluid ends, the valves seat directly against portions of the fluid end. The fluid end is a sizable object that can house two, three, or more valve assemblies, each comprising a suction and discharge valve. Every stroke of the linear force member results in a valve contacting a portion of the fluid end, which must be shaped to match the valve shape and form a seal. This causes wear on the fluid end and valves, which must eventually be replaced. If a valve is damaged, the fluid end cap must be removed and the valve extracted. Specialized tools are frequently needed to extract the valves. Further, the fluid end must be specially designed to fit the shape of the valves. There is a need for a fluid end that does not require such specialized design and handling.

SUMMARY

Embodiments described herein provide a fluid end assembly, comprising a flow box with an inlet manifold having an inlet opening, an outlet manifold having an outlet opening, and a housing between the inlet manifold and the outlet manifold; and a valve cartridge removably disposed in the housing, the valve cartridge comprising a first valve seat at a first end of the cartridge assembly and a second valve seat spaced apart from the first end; a first valve disposed in the cartridge assembly at the first end; a second valve disposed adjacent to the second valve seat; a first resilient member disposed between the first and second valves in contact with the first valve and the second valve; and a second resilient member disposed between the second valve and a second end of the cartridge assembly opposite the first end.

Other embodiments described herein provide a valve cartridge, comprising a cage comprising a first valve seat and a second valve seat; a first valve disposed in the cage, the first valve having a first stem and a first plug portion; a second valve disposed in the cage, the second valve having a second stem and a second plug portion, wherein the second stem is hollow and the first stem fits within the second stem; a first resilient member disposed within the second stem between the first stem and the second plug portion; and a second resilient member disposed between the second plug portion and the cage, wherein the second valve seat is between the first plug portion and the second plug portion.

Other embodiments described herein provide a valve cartridge, comprising a first valve aligned with a second valve; a first valve seat at a first end of the valve cartridge adjacent to the first valve; a second valve seat between the first valve and the second valve; and a resilient member between the first valve and the second valve in contact with the first valve and the second valve.

BRIEF DESCRIPTION OF THE DRAWINGS

So that the manner in which the above-recited features of the present invention can be understood in detail, a more particular description of the invention, briefly summarized above, may be had by reference to embodiments, some of which are illustrated in the appended drawings. It is to be noted, however, that the appended drawings illustrate only typical embodiments of this invention and are therefore not to be considered limiting of its scope, for the invention may admit to other equally effective embodiments.

FIG. 1 is a front view of a fluid end assembly coupled to a pump.

FIG. 2 is a cross-sectional view of a fluid end assembly according to one embodiment.

FIG. 3 is a cross-sectional view of a sleeve used in the fluid end assembly of FIGS. 1 and 2.

FIG. 4A is a cross-sectional view of a fluid end assembly 400 according to another embodiment.

FIG. 4B is a close-up view of the valve cartridge of FIG. 4A.

To facilitate understanding, identical reference numerals have been used, where possible, to designate identical elements that are common to the figures. It is contemplated that elements disclosed in one embodiment may be beneficially utilized on other embodiments without specific recitation.

DETAILED DESCRIPTION

FIG. 1 is a front view of a fluid end assembly 100 coupled to a pump 102. The fluid end assembly 100 includes a flow box 104 with an inlet 106, which is a suction side, and an outlet 108, which is a discharge side. The flow box 104 includes an inlet manifold (not visible in FIG. 1) and an outlet manifold 110. Fluid being pumped flows into the flow box 104 through the inlet 106 into the inlet manifold, through valves to be described further below, into the outlet manifold 110, and through the outlet 108. Piping is typically connected to the inlet 106 and the outlet 108 to carry fluid to and from the flow box 104.

A plurality of valve cartridges 112 is disposed in the flow box 104 dividing the inlet manifold from the outlet manifold 110. In the embodiment of FIG. 1, three valve cartridges 112 are shown, but the fluid end assembly 100 may include any number of valve cartridges 112. A fluid end cap 118 is removably attached to the flow box 104, typically at an upper region thereof, or at the outlet or discharge side thereof, to enclose the fluid end assembly 100. When the fluid end cap 118 is removed, the valve cartridges 112 are removable from the flow box 104 by lifting the valve cartridges 112 from the flow box 104 through the outlet manifold.

The fluid end assembly 100 is coupled to a casing 114 of the pump at a force end 116 thereof. The fluid end assembly 100 has a plurality of openings (not visible in FIG. 1) for accommodating linear force members disposed in the pump casing 114 such that the linear force members can apply pressure to fluid inside the fluid end assembly 100. The linear force members are coupled to a power module 120, which may include a crankshaft. The power module 120 causes the linear force members to reciprocate, extending toward and away from the fluid end 104 through an adapter 122. Openings (not visible) in the adapter 122 register with the openings in the flow box 104 to allow the linear force members to pressurize fluid in the flow box 104.

FIG. 2 is a cross-sectional view of one of the valve cartridges 112 in operating position in the flow box 104. The valve cartridge 112 includes a first valve 201 and a second valve 200. The first valve 201 is disposed in a sleeve 206, at a first end 210 thereof, and the second valve 200 is disposed adjacent to a second end 212 of the sleeve 206. The sleeve 206 is disposed in a housing 208 in the flow box 104. The sleeve 206 is a cylindrical object with an outer diameter similar to an inner diameter of the housing.

In the embodiment of FIG. 2, a first valve seat 202 is optionally disposed in the first end 210 of the sleeve 206, and a second valve seat 204 is optionally disposed in the second end 212 of the sleeve 206. The first valve seat 202 is disposed between the first valve 201 and the first end 210 of the sleeve 206. The second valve seat 204 is disposed between the second valve 200 and the second end 212 of the sleeve 206. The valve seats 202 and 204 each have a seating surface 203 that engages a seating surface 205 of each valve 201 and 200.

The first end 210 of the sleeve 206 has a lip 214 that extends radially inward from the first end 210. The second end 212 of the sleeve 206 has a lip 216 that extends radially outward from the second end 212. Each valve seat 202 and 204 has a lip 215 that extends radially outward and engages a portion of the sleeve 206 to stabilize the valve seat. At the first end 210 of the sleeve 206, the lip 215 of the first valve seat 202 engages the lip 214 at the first end 210 of the sleeve 206. At the second end 212 of the sleeve 206, the lip 215 of the second valve seat 204 engages directly with the second end 212 of the sleeve 206. The first valve 201 thus operates inside the sleeve 206 while the second valve 200 operates outside, and adjacent to the sleeve 206.

The valve seats 202 and 204 are optional because the sleeve 206 may be configured with sealing surfaces to engage the sealing surfaces 205 of the valves directly. For example, valve landings (not shown in FIG. 2) may be shaped directly into the wall of the sleeve 206 at appropriate locations to provide sealing surfaces to engage the sealing surfaces 205 of the valves. Further description of such optional sealing surfaces is provided below in connection with FIG. 3.

The sleeve 206 has an opening 213 in registration with an opening (not shown) in the flow box 104 to allow fluid communication to the power adaptor 122 (FIG. 1). The opening 213 typically has an axis orthogonal to a general direction of fluid flow through the valve cartridge 112.

Each of the first valve seat 202 and the second valve seat 204 has a first end 218 and a second end 220. In the embodiment of FIG. 2, the first end 218 of each valve seat has a diameter greater than a diameter at the second end 220. The lip 215 of each valve seat has a planar surface 224 extending along a plane perpendicular to an axis of the valve cartridge 112, which is also an axis of movement of the valves 200 and 201, and the axis of general fluid flow through the valve cartridge 112. Each valve 200 and 201 moves along its axis, and the axis of the sleeve 206 substantially corresponds with the axes of the valves 202 and 204.

Each valve seat 202 and 204 also has a tapered side 226 that extends from the lip 215 at the first end 218 to the second end 220. The lip 215 protrudes radially outward from the tapered side 226 such that the planar surface 224 and the tapered side 226 define an angle. The tapered side 226 has a diameter that declines monotonically from the first end 218 to the second end 220. The decline may be linear, may include a linear section, or may be non-linear. Each valve seat 202 and 204 remains substantially concentric with the overall axis of the valve along its length.

The tapered side 226 of each valve seat 202 and 204 provides additional stabilization of the valve seat, if desired. The lip 215 of the first valve seat 202 engages with the lip 214 of the sleeve 206 along the planar surface 224. Additionally, and optionally, the tapered side 226 of the first valve seat 202 may engage with an inner surface of the lip 214 at the first end 210. The lip 214 has a tapered inner surface 228 that matches the tapered side 226 of the first valve seat 202 and a planar surface 230 that matches the planar surface 224 of the first valve seat 202. The tapered surfaces of the first valve seat 202 and the lip 214 are optional features. In alternate embodiments, each of the tapered side 226 of the first valve seat 202 and the tapered inner surface 228 of the lip 214 may be untapered, i.e. vertical in the view of FIG. 2. Alternately, the tapered surfaces of the first valve seat 202 and the lip 214 may be tapered in different ways or at different angles, or one may be vertical while the other is tapered. Additionally, the side 226 of the valve seat (tapered or untapered) and the inner surface 228 of the lip 214 (tapered or untapered) may define a gap, such that the valve seat 202 engages the lip 214 only at the planar surface 224.

The second valve seat 204 engages directly with the second end 212 of the sleeve 206. In the embodiment of FIG. 2, the second valve seat 204 also optionally engages an inner wall 232 of the sleeve 206 at the second end 212. The inner wall 232 is tapered to match the tapered side 226 of the second valve seat 204. The second end 212 of the sleeve 206 also has a planar surface 234 that matches the planar surface 224 of the lip 215 of the second valve seat 204.

As with the first valve seat 202, the side 226 of the second valve seat 204, and the inner wall 232 of the sleeve 206, may alternately be any combination of tapered and untapered, and may define a gap such that the second valve seat 204 engages with the second end 212 of the sleeve 206 only at the planar surface 224 of the lip 215.

It should be noted that the lip 215 of the first valve seat 202 may have a radial extent different from the lip 215 of the second valve seat 204. Likewise, the tapered side 226 of the first valve seat 202 may have a different taper from the tapered side 226 of the second valve seat 204, which may differ in any or all of linearity, non-linearity, and angle.

Each of the first and second valves 201 and 200 is biased closed by a valve restraint 240. In FIG. 2, the valve restraints 240 are springs. The valve restraint 240 coupled to the first valve 201 is coupled between a rear 217 of the first valve 201 and a stem 242 of the second valve 200. The valve restraint 240 coupled between the first and second valves 201 and 200 is disposed around a rear stem 219 extending from the rear 217 of the first valve 201 and around the stem 242 of the second valve 200 which extends from the front of the second valve 200 toward the first valve 201 through the interior of the sleeve 206. When the first valve 201 opens due to declining pressure between the first and second valves 201 and 200, the second valve 200 remains closed and provides a biasing force through the valve restraint 240 between the first and second valves 201 and 200 such that when pressure between the first and second valves 201 and 200 equalizes, the biasing force urges the first valve 201 to seat in the first end 210 of the sleeve 206, stopping fluid flow into the valve cartridge 112 from the inlet manifold 251.

The valve restraint 240 coupled to the second valve 200 is coupled to the rear 217 of the second valve 200 around the rear stem 219 of the second valve 200. The valve restraint 240 coupled to the rear 217 of the second valve 200 may be coupled between the rear 217 of the second valve 200 and a valve cap 244, which may be attached to the sleeve 206. The valve cap 244 includes a collar 248 that removably engages with the sleeve 206 at the second end 212 thereof by any convenient means such as press fitting, snap fitting, or threading (in the embodiment of FIG. 2 the collar 248 engages with the second end 212 of the sleeve 206 by a snap fit) and a crown (not visible in the cross-sectional view of FIG. 2) that extends from the collar 248 around the rear stem 219 of the second valve 200 to back-stop the valve restraint 240 disposed around the rear stem 219 of the second valve 200.

The valve restraint 240 coupled to the rear 217 of the second valve 200 provides a biasing force to the second valve 200, supported by the crown of the valve cap 244. When the second valve 200 opens due to increasing pressure between the first and second valves 201 and 200, the valve restraint 240 coupled to the rear 217 of the second valve 200 compresses and the biasing force increases. As the second valve 200 moves away from the first valve 201, the valve restraint 240 coupled between the first and second valves 201 and 200 may lose contact with the second valve 200 at the stem 242. As pressure between the first and second valves 201 and 200 equalizes, the biasing force on the second valve 200 urges the second valve 200 to seat in the second end 212 of the sleeve 206 (i.e. in the second valve seat 204 in the embodiment of FIG. 2), and the stem 242 moves back into contact with, or close proximity to, the valve restraint 240 between the first and second valves 201 and 200.

The valve cartridge 112 is held in place inside the housing 208 by a cartridge restraint 246. The collar 248 of the valve cap 244 may have a landing surface 250 for the cartridge restraint 246 that faces away from the sleeve 206. Alternately, the cartridge restraint 246 may contact the sleeve 206 directly at the planar surface 234 or the lip 216. Seals 252 may be provided at the first and second ends 210 and 212 of the sleeve 206 where the two ends of the sleeve 206 contact the housing 208. Compression is maintained on the seals 252 by action of the cartridge restraint 246, which is compressed between the fluid end cap 108 (not shown in FIG. 2) and the sleeve 206.

FIG. 3 is a cross-sectional view of the sleeve 206 of the valve cartridge 112 of FIG. 2. The tapered inner wall 232 (which is optional as described above) of the sleeve 206 has a first diameter at a first end 302 of the tapered inner wall 232 and a second diameter at a second end 304 of the tapered inner wall 232. The first end 302 of the tapered inner wall 232 is at the second end 212 of the sleeve 206, and the second end 304 connects to a second inner wall 306 of the sleeve 206. The second diameter is less than the first diameter due to the taper of the tapered inner wall 232. The second inner wall 306 has a diameter that may be the same as, or different from, the second diameter, either larger or smaller. In the embodiment of FIG. 3, the diameter of the second inner wall 306 is the same as the second diameter.

The opening 213 of the sleeve 206 is formed through the wall of the sleeve 206, and generally has a diameter less than an outer diameter of the sleeve 206. The diameter of the opening 213 may be the same as, or different from, the diameter of the second inner wall 306. In the embodiment of FIG. 3, the opening 213 has a diameter that is greater than the diameter of the second inner wall 306 such that the second inner wall 306 connects to a curved inner wall 308, which has a radius of curvature equal to the radius of the opening 213. The curved inner wall 308 joins a fourth inner wall 310 which, in the embodiment of FIG. 3, has a constant diameter substantially equal to the diameter of the opening 213. The fourth inner wall 310 extends from the point of joining with the curved inner wall 308 to the lip 214 at the first end 210 of the sleeve 206. Thus, proceeding from the second end 212 of the sleeve 206 to the first end 210 of the sleeve 206 is the tapered inner wall 232, then the second inner wall 306, then the curved inner wall 308, then the fourth inner wall 310. It should be noted that fourth inner wall 310 may have a diameter that is the same as, or different from, the diameter of the opening 213, so long as the fourth inner wall 310 has a length selected to avoid obstructing the opening 213. Thus, the fourth inner wall 310 may have a diameter greater than the diameter of the opening 213. Alternately, the fourth inner wall 310 may have a diameter less than the diameter of the opening 213 if the curved inner wall 308 is extended around the periphery of the opening 213 to join the fourth inner wall 310.

As noted above, the separate valve seats 202 and 204 of the valve cartridge 112 are optional. Shown in phantom in FIG. 3 are optional valve seats formed in the sleeve 206. A first valve seat 312 is shown at the first end 210 and a second valve seat 214 is shown at the second end 212. The first valve seat 312 has a seating surface 316 to engage the seating surface 205 of the first valve 201. The seating surface 316 is angled, or otherwise shaped, to match the seating surface 205 of the first valve 201 to provide an operative seal when the first valve 201 is closed. The second valve seat 214 likewise has a seating surface 318 that is angled to match the seating surface 205 of the second valve 200. In each case, the sleeve 206 is shown with an interior wall 320 that is different from the tapered inner wall 232 and the second inner wall 306. As shown in phantom the alternative interior wall 320 of the sleeve 206 is has a diameter that is equal to a minimum diameter of the seating surfaces 316 and 318. In the case of the seating surface 318, the interior wall 320 of the sleeve 206 is shown having a constant diameter from the seating surface 318 to the opening 213. For the seating surface 316, the interior wall 320 extending from the seating surface 316 to the first end 210 Is shown with constant diameter from the seating surface 316 to the first end 210. Although such features (constant diameter interior wall) simplify manufacture of the sleeve 206, the constant diameter of the interior wall extending from the seating surfaces 316 and 318 is optional. The interior wall 320 may be shaped in any convenient way to promote flow of fluid through the valve cartridge 112, pressure operation of the valves 200 and 201, or for any other reason.

The sleeve 206 may be made from any material with structural strength to withstand operating pressures and forces experienced inside the fluid end 100 and chemically resistant to fluids flowing through the fluid end 100. In some cases, the sleeve 206 may be made of a tough plastic such as polypropylene, polystyrene (for example high impact polystyrene), polybenzimidazole, or hard styrenic polymers such as acrylonitrile butadiene styrene terpolymer. In other cases, the sleeve 206 may be made of any appropriate metal. The various features of the sleeve 206 may be accomplished by molding and/or by machining according to standard practices known in the art.

FIG. 4A is a cross-sectional view of a fluid end assembly 400 according to another embodiment. FIG. 4B is a close-up view of the valve cartridge of FIG. 4A. The flow box 104 is the same as in FIG. 1, with the inlet 106, outlet 108, and outlet manifold 110. Here, the inlet manifold is visible, labelled 402. In the example of FIG. 4, the fluid end assembly 400 is shown with a cap 403 in place covering the outlet manifold 110. An inner wall 401 separates the inlet manifold 402 from the outlet manifold 110 and a plurality of openings 405 provide fluid flow pathways from the inlet manifold 402 through the inner wall 401 into the outlet manifold 110.

Three valve cartridges 404 of a different design from the valve cartridge 112 are disposed in the fluid end assembly 400. As noted above, the fluid end assembly 400 can be configured with any convenient number of valve cartridges 404 to match the number of linear force members. Each valve cartridge 404 fits in a housing 407 formed in the inner wall 401. Each housing 407 is coaxial with one of the openings 405.

Each valve cartridge 404 features a first valve 406 and a second valve 408. The first and second valves 406 and 408 are engaged in a telescoping relationship. The second valve 408 has a hollow stem 410 with an inner diameter 412. The first valve 406 also has a stem 414, shown here as a solid stem, but which may also be hollow. The stem 414 of the first valve 406 thus moves within the stem 410 of the second valve 408. The first and second valves 406 and 408 have respective plug portions 416 and 418 coupled to their respective stems 414 and 410. The stem 410 and the stem 414 may be sized with lengths such that an end 420 of the stem 410 contacts the plug portion 416 of the first valve 406 to define a maximum travel of the stem 414 within the stem 410. A plurality of openings 422, in this case horizontal (i.e. perpendicular to the movement axis of the first and second valves 406 and 408), are provided in the second valve 408 near where the stem 410 meets the plug portion 418 of the second valve 408 to provide hydrostatic balancing as the stem 414 moves within the stem 410. Here, there are four openings 422, but any convenient number of openings 422 may be provided. For example one, two, or three openings 422 may be provided, or more than four openings 422 may be provided. Additionally, one, more than one, or all the openings may be angled in any convenient manner, for example toward or away from the first valve 406. The hollow stem 410 of the second valve 408 is bored axially to a depth that provides a desired travel for the stem 414 within the stem 410.

The first and second valves 406 and 408 are housed in a cage 424. The cage has an upper portion 426 and a lower portion 428. The lower portion 428 includes a first seat 430 for the first valve 406 and a second seat 432 for the second valve. A plurality of posts 434 connect the first seat 430 to the second seat 432 to provide structural strength for the lower portion 428. The plug portion 416 of the first valve 406 travels within the lower portion 428 of the cage 424, while the plug portion 418 of the second valve 408 travels within the upper portion 426 of the cage 424. The upper portion 426 of the cage features a top plate 434 that provides structural strength for the valve cartridge 404, and may, in some cases, provide a contact surface for the cap 403. Here, a gap 435 is provided between the top plate 434 and the cap 403.

The cage 424 can be molded as one piece including the upper portion 426 and the lower portion 428 in a single molded article. Alternately, the upper and lower portions 426 and 428 can be separately molded and then welded together. For example, the posts of the upper portion can be welded to the second seat 432. The cage 424 can generally be made of structurally strong plastic or metal selected based on loading, cycling, and chemistry of anticipated service. The example plastics listed above in connection with the sleeve of FIG. 3 can also be used for the cage 424.

The lower portion 428 of the cage 424 fits within the housing 407. The first seat 430 contacts a floor 444 of the housing 407 such that the first seat 430 is adjacent to the opening 405. The first seat 430 has an inner wall 429 with a dimension that is substantially the same as a dimension of an inner wall 431 of the opening 405. It should be noted, however, that flow characteristics of the fluid end assembly 400 can be changed by using a valve cartridge with a first seat that has an inner wall with dimension different from that of the inner wall 431 of the opening 405. For example, if the dimension of the inner wall of the first seat is smaller than the dimension of the inner wall 431 of the opening 405, flow through the fluid end assembly 400 can be constrained. Such flow characteristics can be changed by swapping a first valve cartridge having a first flow rating with a second valve cartridge having a second flow rating different from the first flow rating, without changing any other pump hardware.

The housing 407 has a first portion 446 and a second portion 448. The first portion 446 extends from the floor 444 to the second portion 448. The first portion 446 has an inner wall 447 with a dimension larger than the dimension of the inner wall 431 of the opening 405. The second portion 448 has an inner wall 449 with dimension larger than the dimension of the inner wall 447 of the first portion 446. As described above, the first seat 430 contacts the floor 444 of the housing 407. The first seat 430 has an outer wall 450 with a dimension that is smaller than the dimension of the inner wall 447 of the first portion 446, so the first seat 430 contacts the housing 407 only at the floor 444 thereof. The second seat 432 has an outer wall 452 with a dimension larger than the dimension of the outer wall 450 of the first seat 430 and larger than the inner diameter 447 of the first portion 446. The outer diameter 452 is substantially the same as the inner diameter 449 of the second portion 448 such that the second seat 432 contacts the second portion 448 at a sidewall thereof. The first portion 446 and the second portion 448 together define a shelf 454 that extends from a side wall of the first portion 446, at the top end of the first portion 446, to the side wall of the second portion 448, at the bottom end of the second portion 448. The second seat 432 also contacts the shelf 454, and thus provides a snug fit of the second seat 432 within the second portion 448 of housing 407 at the shelf 454.

A first seal member 460 is disposed in a groove 462 along the bottom surface of the lower portion 428, which contacts the floor 444 of the housing 407, to provide a first seal between the valve cartridge 404 and the inner wall 401. A second seal member 464 is provided in a groove 467 around the periphery of the second seat 432, where the second seat 432 contacts the side wall of the second portion

The second valve 408 has a rear stem 436 oriented toward the top plate 434. The top plate 434 has an alignment bore 438 that extends from an inner surface of the top plate 434 toward the plug portion 418 of the second valve 408. The rear stem 436 is inserted into the alignment bore 438 of the top plate 434, and travels within the alignment bore 438 to maintain alignment of the first and second valves 406 and 408. In this case, the second valve 408 can travel until the plug portion 418 of the second valve 408 contacts an end 440 of the alignment bore 438. At that time, the rear stem 436 protrudes above the top plate 434 into the gap 435. Length of the alignment bore 438 is selected to provide sufficient travel for the second valve 408 based on flow characteristics needed for the valve cartridge. Thickness of the top plate 434 can be varied to optimize structural strength and cost. The top plate 434 is connected to the second seat 432 by a plurality of posts 442 that provide structural strength for the upper portion 426 while allowing fluid flow through the upper portion 426 into the outlet manifold 110.

While the foregoing is directed to embodiments of the invention, other and further embodiments of the invention may be devised without departing from the basic scope thereof. 

What is claimed is:
 1. A fluid end assembly, comprising: a flow box with an inlet manifold having an inlet opening, an outlet manifold having an outlet opening, and a housing between the inlet manifold and the outlet manifold; and a valve cartridge removably disposed in the housing, the valve cartridge comprising: a first valve seat at a first end of the cartridge assembly and a second valve seat spaced apart from the first end; a first valve disposed in the cartridge assembly at the first end; a second valve disposed adjacent to the second valve seat; a first resilient member disposed between the first and second valves in contact with the first valve and the second valve; and a second resilient member disposed between the second valve and a second end of the cartridge assembly opposite the first end.
 2. The fluid end assembly of claim 1, wherein each valve seat engages with a sleeve disposed in the housing.
 3. The fluid end assembly of claim 2, wherein the sleeve has a first lip extending radially inward at a first end of the sleeve, the first valve seat has a lip that extends radially outward, and the lip of the first valve seat engages the first lip.
 4. The fluid end of claim 3, wherein the sleeve has a second end opposite from the first end, the second valve seat has a lip that extends radially outward, and the lip of the second valve seat engages with the second end of the sleeve.
 5. The fluid end of claim 1, wherein the first valve seat is connected to the second valve seat by a plurality of posts.
 6. The fluid end of claim 5, wherein each of the first and second valves has a stem, the stem of the second valve is hollow, and the stem of the first valve is disposed within the stem of the second valve.
 7. The fluid end of claim 6, wherein the first resilient member is disposed within the stem of the second valve.
 8. The fluid end of claim 1, wherein the first valve has a first stem, the second valve has a second stem that is hollow, the first stem fits within the second stem, and the first resilient member is disposed within the second stem.
 9. A valve cartridge, comprising: a cage comprising a first valve seat and a second valve seat; a first valve disposed in the cage, the first valve having a first stem and a first plug portion; a second valve disposed in the cage, the second valve having a second stem and a second plug portion, wherein the second stem is hollow and the first stem fits within the second stem; a first resilient member disposed within the second stem between the first stem and the second plug portion; and a second resilient member disposed between the second plug portion and the cage, wherein the second valve seat is between the first plug portion and the second plug portion.
 10. The valve cartridge of claim 9, wherein the first valve seat and the second valve seat are connected by a plurality of posts.
 11. The valve cartridge of claim 10, wherein the cage further comprises a top plate with an alignment bore, and the second valve has a rear stem that fits within the alignment bore.
 12. The valve cartridge of claim 11, wherein the second resilient member contacts the second plug portion and the top plate.
 13. The valve cartridge of claim 12, further comprising a first groove along a bottom surface of the cage and a second groove around a periphery of the second valve seat.
 14. The valve cartridge of claim 13, wherein the second valve seat is connected to the top plate by a plurality of posts.
 15. A valve cartridge, comprising: a first valve aligned with a second valve; a first valve seat at a first end of the valve cartridge adjacent to the first valve; a second valve seat between the first valve and the second valve; and a resilient member between the first valve and the second valve in contact with the first valve and the second valve.
 16. The valve cartridge of claim 15, further comprising a second resilient member between the second valve and a second end of the valve cartridge opposite from the first end.
 17. The valve cartridge of claim 16, wherein the first valve has a first stem, the second valve has a second stem that is hollow, and the first stem fits within the second stem. 